Residents of a 21-storey condominium tower in downtown Vancouver have been told it could be days before they are able to return home, following the building's evacuation on Saturday.

Many have been living in hotels paid for by the province's emergency program since the building, which used to be the B.C. Hydro building, was evacuated for a second time on Saturday.

The problem started on Thursday when residents first smelled fumes after crews working on a flooring project in the basement of the Electra at 989 Nelson Street used solidifying foam to fill a very large gap in the concrete that did not appear on any building plans.

The foam usually becomes hard, but officials said there was so much it started a chemical reaction, and on Friday smoke started to billow out of the building, spreading noxious fumes for several blocks.

The incident caused traffic snarls during Friday afternoon's rush hour and the evacuation of the 242-suite building along with several nearby, but residents were allowed back in on Friday night.

But then on Saturday fire crews noticed more fumes and evacuated the building once again. The residents have not been able to return since, even to pick up medical items, cash or identification.

Unclear what to test for

Nelson Street outside the building remained closed to traffic on Monday while officials continued to investigate. Vancouver's deputy city manager Sadhu Johnston pleaded with the public for patience at a morning briefing.

The evacuation of the Electra condominium building at Burrard Street and Nelson Street, formerly the BC Hydro headquarters, remained in force Monday. (CBC) "At this point…we do not know how long people will be out of their suites. We are asking folks to plan for at least a couple more days," said Johnston.

City officials said the contractor is cooperating with its investigation, but part of the problem is no one knows what chemicals to test for.

One suspected chemical contaminate is hydrogen cyanide, but deputy Vancouver Fire Chief Nick Delmonico said at this point there are no similar incidents to draw lessons from on how to proceed.

"I think at this point that appears to be the problem — we don't have a history of this happening — so that's the ongoing task for these gentleman is to find that out, and search a little deeper," he said.

Residents and health officials are both concerned about the noxious fumes, and if they will linger in the carpets, curtains, and other parts of the suites.

With files from The Canadian Press